Flexible display panel

ABSTRACT

A flexible display panel includes a bending area and a surrounding area adjacent to the bending area. The barrier layer includes first silicon nitride layers and first silicon oxide layers which are overlapped with the bending area. The first silicon nitride layers and the first silicon oxide layers are stacked alternately. Each of the first silicon nitride layers may have a thickness less than or equal to about 400 Å, and each of the first silicon oxide layers may have a thickness less than or equal to about 650 Å.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. patent application Ser. No.14/806,556, filed Jul. 22, 2015, which claims priority to and thebenefit of Korean Patent Application No. 10-2014-0117214, filed on Sep.3, 2014, the entire contents of both of which are incorporated herein byreference.

BACKGROUND

The present disclosure herein relates to a flexible display panel.

Recently, bendable or foldable display panels (hereinafter referred toas flexible display panels) are being further developed. Such a flexibledisplay panel includes a flexible display panel and various functionalmembers.

Typically, the flexible display panel includes a base member, variousfunctional layers located on the base member, and pixels located on thebase member.

SUMMARY

The present disclosure provides a flexible display panel having reduceddefects.

Embodiments of the inventive concept provide flexible display panelsincluding a base member, a barrier layer, and a pixel. The barrier layermay be located on the base member, and may include first silicon nitridelayers and first silicon oxide layers which are stacked alternately. Thepixel may be located on the barrier layer, and may include a thin filmtransistor and a display element connected to the thin film transistor.The first silicon nitride layers each may have a thickness less than orequal to about 400 Å, and the first silicon oxide layers each may have athickness less than or equal to about 650 Å.

In some embodiments, a total thickness of the first silicon oxide layersmay range from about 500 Å to about 10,000 Å. Herein, a total thicknessof the first silicon nitride layers may be less than that of the firstsilicon oxide layers.

In other embodiments, a flexible display panel according to anembodiment of the inventive concept includes a bending area and asurrounding area adjacent to the bending area. The barrier layerincludes first silicon nitride layers and first silicon oxide layerswhich are overlapped with the bending area. The first silicon nitridelayers and the first silicon oxide layers are stacked alternately. Thebarrier layer includes at least one second silicon nitride layeroverlapped with the surrounding area and at least one second siliconoxide layer overlapped with the second silicon nitride layer.

In still other embodiments, each of the first silicon nitride layers mayhave a thickness less than or equal to about 400 Å, and each of thefirst silicon oxide layers may have a thickness less than or equal toabout 650 Å. The second silicon nitride layer has a thickness greaterthan those of the first silicon nitride layers, and the second siliconoxide layer has a thickness greater than those of the first siliconoxide layers.

In even other embodiments, a flexible display panel according to anembodiment of the inventive concept may further include a boundary areadefined between the bending area and the surrounding area. The firstsilicon nitride layers and the first silicon oxide layers may be spacedfrom the second silicon nitride layer and the second silicon oxide layerwith the boundary layer disposed therebetween.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are included to provide a furtherunderstanding of the inventive concept, and are incorporated in andconstitute a part of this specification. The drawings illustrateexemplary embodiments of the inventive concept and, together with thedescription, serve to explain principles of the inventive concept. Inthe drawings:

FIG. 1 is a perspective view illustrating a flexible display panelaccording to an embodiment of the inventive concept;

FIG. 2 is a side view illustrating an unfolded state of a flexibledisplay panel according to an embodiment of the inventive concept;

FIG. 3 is a side view illustrating a folded state of a flexible displaypanel according to an embodiment of the inventive concept;

FIG. 4 is a plan view illustrating a portion of a flexible display panelaccording to an embodiment of the inventive concept;

FIG. 5 is an equivalent circuit diagram of a pixel of a flexible displaypanel according to an embodiment of the inventive concept;

FIG. 6 is a layout of a pixel according to an embodiment of theinventive concept;

FIG. 7 is a sectional view taken along line I-I′ in FIG. 6;

FIG. 8 is a sectional view taken along line II-II′ in FIG. 6;

FIG. 9 is an expanded view of a barrier layer in FIG. 6;

FIG. 10 is an expanded view of a buffer layer in FIG. 6;

FIGS. 11A and 11B are expanded views of barrier layers according to anembodiment of the inventive concept;

FIGS. 12A and 12B are expanded views of buffer layers according to anembodiment of the inventive concept; and

FIG. 13 is an expanded view of a barrier layer according to anembodiment of the inventive concept.

DETAILED DESCRIPTION

Hereinafter, a flexible display panel according to an embodiment of theinventive concept will be described with reference to the accompanyingdrawings.

In the drawings, scales of some elements are exaggerated or reduced toclearly illustrate a plurality of layers and areas. Like referencenumerals or symbols refer to like elements throughout. And, it will alsobe understood that when a layer (or film) is referred to as being conyanother layer or substrate, it may be directly on the other layer orsubstrate, or intervening layers may also be present. Furthermore,although one surface of a layer is illustrated to be flat, it is notnecessarily required to be flat but a stepped portion may be exist on asurface of an upper layer due to a surface morphology of an underlyinglayer during a stacking process.

FIG. 1 is a perspective view illustrating a flexible display panelaccording to an embodiment of the inventive concept. FIG. 2 is a sideview illustrating an unfolded state of a flexible display panelaccording to an embodiment of the inventive concept. FIG. 3 is a sideview illustrating a bent state of a flexible display panel according toan embodiment of the inventive concept.

As illustrated in FIGS. 1 to 3, a flexible display panel DP according toan embodiment of the inventive concept includes a bending area FA andsurrounding areas SA. The bending area FA is defined as an area in whichthe flexible display panel DP is folded. The surrounding areas SA aredefined as areas adjacent to the bending area FA. The surrounding areasSA may be flat or bent gradually.

Each of the bending area FA and the surrounding areas SA includes aplurality of pixels. The bending area FA and the surrounding areas SAcreate an image without distinction. The flexible display panel DP maydisplay an image unidirectionally or bidirectionally.

FIG. 3 illustrates the flexible display panel DP bent according to ausing form. The flexible display panel DP may be completely folded suchthat the two surrounding areas SA face each other. That is, the flexibledisplay panel DP may be folded 180 degrees at the bending area FA.Herein, the flexible display panel DP may have a radius curvature CRranging from about 0.5 mm to about 10 mm. According to another usingform, the flexible display panel DP may be bent in a direction oppositeto that in FIG. 3, and a bending angle is adjustable.

In this embodiment, the flexible display panel DP is exemplarilyillustrated as including one bending area FA, but in an embodiment ofthe inventive concept, the flexible display panel DP may include two ormore bending areas FA. Furthermore, in an embodiment of the inventiveconcept, the flexible display panel DP may be bent or rolled to have acurved surface on the whole. Furthermore, another area may be definedbetween the bending area FA and the surrounding areas SA, and each ofthe surrounding areas SA may be divided into a plurality of areas.

The flexible display panel DP according to the inventive concept may bean organic light emitting display panel, an electrophoresis displaypanel, or an electrowetting display panel, etc. Display panels includedifferent display elements according to their types. Hereinafter, anorganic light emitting display panel that includes an organic lightemitting diode as a display element will be described exemplarily.

FIG. 4 is a plan view illustrating a portion of a flexible display panelaccording to an embodiment of the inventive concept. FIG. 5 is anequivalent circuit diagram of a pixel of a flexible display panelaccording to an embodiment of the inventive concept.

As illustrated in FIG. 4, the flexible display panel DP may be dividedinto a plurality of luminescent areas PXA and a non-luminescent areaNPXA surrounding the plurality of luminescent areas PXA. Each of thebending area FA and the surrounding area SA which are illustrated inFIGS. 1 to 3 includes the plurality of luminescent areas PXA and thenon-luminescent area NPXA.

The plurality of luminescent areas PXA each may be defined as an area inwhich an organic light emitting diode OLED of a pixel PX is overlapped,which will be described later. Also, the non-luminescent area NPXA isdefined as an area in which a circuit or signal lines DL, GL, and KL ofa pixel PX are overlapped.

As illustrated in FIG. 5, the pixel PX includes a first thin filmtransistor TFT1, a second thin film transistor TFT2, a capacitor Cap,and an organic light emitting diode OLED. Alternatively, an equivalentcircuit of the pixel PX is not limited to that in FIG. 5, but may bemodified.

The first thin film transistor TFT1 includes a control electrodeconnected to a gate line GL, an input electrode connected to a data lineDL, and an output electrode. The first thin film transistor TFT1 outputsa data signal applied to the data line DL in response to a gate signalapplied to the gate line GL.

The capacitor Cap includes a first electrode connected to the first thinfilm transistor TFT1 and a second electrode which receives a first powersupply voltage ELVDD. The capacitor Cap charges voltage corresponding tothe data signal received from the first thin film transistor TFT1.

The second thin film transistor TFT2 includes a control electrodeconnected to the output electrode of the first thin film transistor TFT1and the first electrode of the capacitor Cap, an input electrode whichreceives the first power supply voltage ELVDD, and an output electrode.The output electrode of the second thin film transistor TFT2 isconnected to the organic light emitting diode OLED. The second thin filmtransistor TFT2 controls a driving current which flows through theorganic light emitting diode OLED to correspond to voltage charged inthe capacitor Cap.

The organic light emitting diode OLED includes a first electrodeconnected to the second thin film transistor TFT2, and a secondelectrode which receives a second power supply voltage ELVSS.Furthermore, the organic light emitting diode OLED includes an organiclight emitting layer disposed between the first electrode and the secondelectrode. The organic light emitting diode OLED emits light duringturn-on intervals of the second thin film transistor TFT2.

FIG. 6 is a layout of a pixel according to an embodiment of theinventive concept. FIG. 7 is a sectional view taken along line I-I′ inFIG. 6. FIG. 8 is a sectional view taken along line II-II′ in FIG. 6.FIG. 6 illustrates a layout of a pixel corresponding to the equivalentcircuit in FIG. 5. Hereinafter, a flexible display panel will bedescribed in more detail with reference to FIGS. 5 to 7.

The flexible display panel DP includes a base member SUB1, functionallayers BRL and BFL, signal lines GL and DL, a pixel PX, and anencapsulation member SUB2. The constitutions of the base member SUB1,the functional layers BRL and BFL, the signal lines GL and DL, thepixels PX, and the encapsulation member SUB2 may vary with to the typeof the flexible display panel DP

The base member SUB1 may include a flexible plastic substrate made of,for example, polyamide. The functional layers BRL and BFL are located onone surface of the base member SUB1. The functional layers BRL and BFLinclude a barrier layer BRL and a buffer layer BFL. The buffer layer BFLis located on the barrier layer BRL.

The barrier layer BRL prevents or minimizes impurities that exist in thebase member SUB1 from being introduced into the pixel PX duringmanufacturing process. Particularly, the barrier layer BRL prevents theimpurities from diffusing into semiconductor patterns AL1 and AL2 of thepixel PX. The impurities may be introduced from the outside, or may become out by thermal decomposition of the base member SUB1. Theimpurities may be, for example, sodium or gas emitted from the basemember SUB1. Furthermore, the barrier layer BRL blocks moisture frombeing introduced into the pixel PX from the outside.

The buffer layer BFL supplements functions of the barrier layer BRL. Atthe same time, the buffer layer BFL enhances properties of the thin filmtransistors TFT1 and TFT2 as compared with the barrier layer BRL.Further detailed description therefore will be provided later. In anembodiment of the inventive concept, the buffer layer BFL may beomitted.

The signal lines GL and DL and the pixel PX are located on the bufferlayer BFL. A semiconductor pattern AL1 (hereinafter, a firstsemiconductor pattern) of the first thin film transistor TFT1 and asemiconductor pattern AL2 (hereinafter, a second semiconductor pattern)of the second thin film transistor TFT2 are located on the buffer layerBFL. The first semiconductor pattern AL1 and the second semiconductorpattern AL2 may include amorphous silicon formed at low temperature. Inaddition, the first semiconductor pattern AL1 and the secondsemiconductor pattern AL2 may include a metal oxide semiconductor.

A first insulation layer 12, which covers the first semiconductorpattern AL1 and the second semiconductor pattern AL2, is located on thebuffer layer BFL. The first insulation layer 12 includes an organiclayer and/or an inorganic layer. In one embodiment, the first insulationlayer 12 may include a plurality of inorganic thin films. The pluralityof inorganic thin films may include a silicon nitride layer and asilicon oxide layer.

The gate line GL is located on the first insulation layer 12. A controlelectrode GE1 (hereinafter, a first control electrode) of the first thinfilm transistor TFT1 and a control electrode GE2 (hereinafter, a secondcontrol electrode) of the second thin film transistor TFT2 are locatedon the first insulation layer 12.

A first electrode CE1 in the capacitor Cap is located on the firstinsulation layer 12. The first electrode CE1 may be formed along withthe gate line GL through the same photolithography process. In otherwords, the first electrode CE1 and the gate line GL may be made of thesame material.

A second insulation layer 14, which covers the first control electrodeGE1, the second control electrode GE2, and the first electrode CE1, islocated on the first insulation layer 12. The second insulation layer 14includes an organic layer and/or an inorganic layer. Particularly, thesecond insulation layer 14 may include a plurality of inorganic thinfilms. The plurality of inorganic thin films may include a siliconnitride layer and a silicon oxide layer.

The data line DL and a power supply line KL are located on the secondinsulation layer 14. An input electrode SE1 (hereinafter, a first inputelectrode) and an output electrode DE1 (hereinafter, a first outputelectrode) of the first thin film transistor TFT1 are located on thesecond insulation layer 14. An input electrode SE2 (hereinafter, asecond input electrode) and an output electrode DE2 (hereinafter, asecond output electrode) of the second thin film transistor TFT2 arelocated on the second insulation layer 14. The first input electrode SE1is branched from the data line DL. The second input electrode SE2 isbranched from the power supply line KL.

A second electrode CE2 of the capacitor Cap is located on the secondinsulation layer 14. The second electrode CE2 may be formed along withthe data line DL through the same photolithography process and the powersupply line KL, and made of the same material as those of the data lineDL and the source line KL.

The first input electrode SE1 and the first output electrode DE1 areconnected to the first semiconductor pattern AL1 via a firstthrough-hole CH1 and a second through-hole CH2, respectively. Herein,the first through-hole CH1 and the second through-hole CH2 pass throughthe first insulation layer 12 and the second insulation layer 14. Thefirst output electrode DE1 is connected to the first electrode CE1 via athird through-hole CH3 which passes through the second insulation layer14. The second input electrode SE2 and the second output electrode DE2are connected to the second semiconductor pattern AL2 via a fourththrough-hole CH4 and a fifth through-hole CH5, respectively. Herein, thefourth through-hole CH4 and the fifth through-hole CH5 pass through thefirst insulation layer 12 and the second insulation layer 14.Alternatively, in another embodiment of the inventive concept, the firstthin film transistor TFT1 and the second thin film transistor TFT2 maybe modified to have a bottom-gate structure.

A third insulation layer 16, which covers the first input electrode SE1,the first output electrode DE1, the second input electrode SE2, and thesecond output electrode DE2, is located on the second insulation layer14. The third insulation layer 16 includes an organic layer and/or aninorganic layer. Particularly, the third insulation layer 16 may includean organic substance to provide a flat surface.

A pixel defined layer PXL and the organic light emitting diode OLED arelocated on the third insulation layer 16. The organic light emittingdiode OLED includes an anode AE, a first common layer CL1, an organiclight emitting layer EML, a second common layer CL2, and a cathode CEwhich are stacked in sequence. The anode AE is connected to the secondoutput electrode DE2 via a sixth through-hole CH6 which passes throughthe third insulation layer 16. Positions of the anode AE and the cathodeCE in the organic light emitting diode OLED may be changed reversely.

The anode AE is located on the third insulation layer 16. An opening OPof the pixel defined layer PXL exposes the anode AE. The first commonlayer CL1 is located on the anode AE. The first common layer CL1 isdisposed not only in a luminescent area PXA corresponding to the openingOP, but also in a plurality of other luminescent areas PXA (see FIG. 4)and a non-luminescent area NPXA. In other words, the first common layerCL1 is disposed throughout the base member SUB1. The first common layerCL1 includes a hole injection layer. The first common layer CL1 mayfurther include a hole transport layer.

The organic light emitting layer EML is located on the first commonlayer CL1. The organic light emitting layer EML may be located only inan area corresponding to the opening OP. A second common layer CL2 islocated on the organic light emitting layer EML. The second common layerCL2 is disposed throughout the base member SUB1 like the first commonlayer CL1. The second common layer CL2 includes an electron injectionlayer. The second common layer CL2 may further include an electrontransport layer. The cathode CE is located on the second common layerCL2. The cathode CE is disposed throughout the base member SUB1.

An encapsulation layer 18 is located on the cathode CE. Theencapsulation layer 18 may include a plurality of thin filmencapsulation layers. The thin film encapsulation layers may include asilicon nitride layer and a silicon oxide layer.

The display panel DP may include another substrate SUB2 which faces thebase member SUB1. The other substrate SUB2 may be an encapsulationsubstrate which protects the plurality of pixels PX.

In one embodiment, a protective film may be located on the other surfacethat faces the one surface of the base member SUB1 on which thefunctional layers BRL and BFL are disposed. The protective film mayprotect the pixel PX from the external impact.

FIG. 9 is an expanded view of the barrier layer in FIG. 6. Hereinafter,the barrier layer will be described in detail with reference to FIG. 9.

The barrier layer BRL includes silicon nitride layers SN1-1 to SN1-n(hereinafter, first silicon nitride layers) and silicon oxide layersSO1-1 to SO1-n (hereinafter, first silicon oxide layers) which arestacked alternately. The barrier layer BRL may be provided by means ofchemical vapor deposition, thermal deposition, sputtering, or the like.

Bending stiffness of a single layer is expressed as Equation 1.BS∝E×TH ³  (1)

where BS is a bending stiffness, E is an elastic modulus, and TH is athickness of a single layer.

The bending stiffness of a barrier layer having the single layerstructure is proportional to the cube of thickness. On the other hand,the bending stiffness of a barrier layer BRL that includes the firstsilicon nitride layers SN1-1 to SN1-n and the first silicon oxide layersSO1-1 to SO1-n is equal to the sum of respective bending stiffnesses ofthe first silicon nitride layers SN1-1 to SN1-n and the first siliconoxide layers SO1-1 to SO1-n. Therefore, the barrier layer BRL accordingto this embodiment may have a lower bending stiffness than a barrierlayer having a single layer structure.

In general, a single layer is deformed by applied stress. Accordingly,if bending stress (tensile stress or compressive stress) is greater thanyield strength, then the single layer is immediately fractured. If thesingle layer has a thickness less than a certain thickness, then it hasplasticity in a predetermined range even though bending stress greaterthan yield strength is applied thereto. The thickness allowing thesingle layer to have the plasticity depends on a substance whichconstitutes the single layer. The thickness of the single layer havingthe plasticity may be calculated by Equation 2.

$\begin{matrix}{h^{*} \approx {\alpha^{2}\frac{\gamma \times E}{\sigma_{th}^{2}}}} & (2)\end{matrix}$

where h* is a thickness of a single layer, α is a parameter depending onthe crack geometry, γ is a surface energy, E is a Young's modulus, σ isa theoretical strength. σ is equal to E/30.

Silicon nitride and silicon oxide have physical properties as shown inthe following Table 1. The maximum thickness of the silicon nitridelayer having the plasticity is 400 Å as calculated according to Equation2. Likewise, the maximum thickness of the silicon oxide layer having theplasticity is 650 Å as calculated according to Equation 2.

TABLE 1 α, parameter γ, σ, depending on the surface E, Young'stheoretical crack geometry energy modulus strength Silicon nitride{square root over (π)}   1 J/m² 76.5 GPa   2.55 GPa Silicon oxide{square root over (π)} 1.6 J/m² 82 GPa  2.7 GPa

In one embodiment, in order for the barrier layer BRL according to thisembodiment to have plasticity in a predetermined range even thoughbending stress greater than yield strength is applied thereto, each ofthe first silicon nitride layers SN1-1 to SN1-n has a thickness TH1 lessthan or equal to about 400 Å. For the same reason, in one embodimenteach of the first silicon oxide layers SO1-1 to SO1-n has a thicknessTH2 less than or equal to about 650 Å.

The first silicon nitride layers SN1-1 to SN1-n and the first siliconoxide layers SO1-1 to SO1-n which have above-described thicknesses TH1and TH2 have plasticity even though bending stress greater than yieldstrength occurs. Therefore, even though bending stress greater thanyield strength is applied to the barrier layer BRL, fracture of thebarrier layer BRL may be prevented.

The sum of thicknesses TH2 of the first silicon oxide layers SO1-1 toSO1-n included in the barrier layer BRL may have a range of about 500 Åto about 10,000 Å. The sum of thicknesses TH1 of the first siliconnitride layers SN1-1 to SN1-n included in the barrier layer BRL is lessthan the sum of thicknesses TH2 of the first silicon oxide layers SO1-1to SO1-n. In consideration of impurities/moisture blocking function ofthe barrier layer BRL, the thicknesses TH1 of the first silicon nitridelayers SN1-1 to SN1-n and the thicknesses TH2 of the silicon oxidelayers SO1-1 to SO1-n may be varied within the above range. Furthermore,in consideration of a deposition time and manufacturing costs for thebarrier layer BRL, the thicknesses TH1 of the first silicon nitridelayers SN1-1 to SN1-n and the thicknesses TH2 of the first silicon oxidelayers SO1-1 to SO1-n may be varied within the above range.

Herein, the first silicon nitride layers SN1-1 to SN1-n may have thesame thickness. Likewise, the first silicon oxide layers SO1-1 to SO1-nmay have the same thickness. The number of stacks of the first siliconnitride layers SN1-1 to SN1-n and the first silicon oxide layers SO1-1to SO1-n may be changed variously in consideration of the thickness ofthe barrier layer BRL, the thicknesses of the first silicon nitridelayers SN1-1 to SN1-n, and the thicknesses of the first silicon oxidelayers SO1-1 to SO1-n.

For example, the flexible display panel DP may include a barrier layerBRL with a thickness of 3,500 Å which includes ten first silicon nitridelayers SN1-1 to SN1-10, each having a thickness of 50 Å, and ten firstsilicon oxide layers SO1-1 to SO1-10, each having a thickness of 300 Å.Alternatively, the flexible display panel DP may include a barrier layerwith a thickness of 2,550 Å which includes three first silicon nitridelayers SN1-1 to SN1-3, each having a thickness of 200 Å, and three firstsilicon oxide layers SO1-1 to SO1-3, each having a thickness of 650 Å.Alternatively, the flexible display panel DP may include a barrier layerwith a thickness of 5,600 Å which includes ten first silicon nitridelayers SN1-1 to SN1-10, each having a thickness of 60 Å, and ten firstsilicon oxide layers SO1-1 to SO1-10, each having a thickness of 500 Å.

Alternatively, the flexible display panel DP may include a barrier layerwith a thickness of 3,750 Å which includes three first silicon nitridelayers SN1-1 to SN1-3, each having a thickness of 100 Å, three firstsilicon nitride layers SN1-4 to SN1-6, each having a thickness of 200 Å,three first silicon oxide layers SO1-1 to SO1-3, each having a thicknessof 300 Å, and three first silicon oxide layers SO1-4 to SO1-6, eachhaving a thickness of 650 Å.

According to the above-described barrier layers, a total thickness ofthe first silicon oxide layers SO1-1 to SO1-n is greater than that ofthe first silicon nitride layers SN1-1 to SN1-n. Silicon oxide has agreater moisture blocking efficiency than silicon nitride. The barrierlayers include more amount of silicon oxide than silicon nitride toenhance the moisture block efficiency.

FIG. 10 is an expanded view of the buffer layer in FIG. 6. Hereinafter,the buffer layer will be described in detail with reference to FIG. 10.

The buffer layer BFL includes silicon nitride layers SN2-1 to SN2-m(hereinafter, second silicon nitride layers) and silicon oxide layersSO2-1 to SO2-m (hereinafter, second silicon oxide layers) which arestacked alternately. The buffer layer BFL may be provided by means ofchemical vapor deposition, thermal deposition, sputtering, or the like.

As described with reference to above Equation 1, the buffer layer BFLhaving a multi-layer structure may have a lower bending stiffness than abuffer layer having a single layer structure although they have the samethickness. As described with reference to above Equation 2, for the samereason as the first silicon nitride layers SN1-1 to SN1-n and the firstsilicon oxide layers SO1-1 to SO1-n, each of the second silicon nitridelayers SN2-1 to SN2-m has a thickness TH3 less than or equal to about400 Å, and each of the second silicon oxide layers SO2-1 to SO2-m has athickness TH4 less than or equal to about 650 Å.

The sum of thicknesses TH3 of the second silicon nitride layers SN2-1 toSN2-m included in the buffer layer BFL may have a range of about 500 Åto about 10,000 Å. The sum of thicknesses TH4 of the second siliconoxide layers SO2-1 to SO2-m included in the buffer layer BFL may be lessthan the sum of thicknesses TH3 of the second silicon nitride layersSN2-1 to SN2-m.

In one embodiment, the second silicon nitride layers SN2-1 to SN2-m mayhave the same thickness. Likewise, the second silicon oxide layers SO2-1to SO2-m may have the same thickness. The number of stacks of the secondsilicon nitride layers SN2-1 to SN2-m and the second silicon oxidelayers SO2-1 to SO2-m may be changed variously considering the thicknessof the buffer layer BFL, the thicknesses of the second silicon nitridelayers SN2-1 to SN2-m, and the thicknesses of the second silicon oxidelayers SO2-1 to SO2-m.

For example, the flexible display panel DP may include a buffer layerBFL with a thickness of 2,500 Å which includes ten second siliconnitride layers SN2-1 to SN2-10, each having a thickness of 200 Å, andten second silicon oxide layers SO2-1 to SO2-10, each having a thicknessof 50 Å. Alternatively, the flexible display panel DP may include abuffer layer BFL with a thickness of 3,600 Å which includes five secondsilicon nitride layers SN2-1 to SN2-5, each having a thickness of 500 Å,five second silicon nitride layers SN2-6 to SN2-10, each having athickness of 100 Å, five second silicon oxide layers SO1-1 to SO1-5,each having a thickness of 100 Å, and five second silicon oxide layersSO2-6 to SO2-10, each having a thickness of 20 Å.

According to the above-described buffer layer, a total thickness of thesecond silicon nitride layers SN2-1 to SN2-m is greater than that of thesecond silicon oxide layers SO2-1 to SO2-m. A thin film transistorprovided on a buffer layer that includes more amount of silicon nitridethan silicon oxide has a higher mobility, a lower leakage current, and alower subthreshold swing than a thin film transistor provided on abuffer layer that includes less amount of silicon nitride than siliconoxide.

FIGS. 11A and 11B are expanded views of a barrier layer according to anembodiment of the inventive concept. Hereinafter, a barrier layer willbe described in detail with reference to FIGS. 11A and 11B.

As illustrated in FIG. 11A, a barrier layer BRL-1 according to thisembodiment has different layer structures by area. The barrier layerBRL-1 includes silicon nitride layers SN3-1 to SN3-n (hereinafter, thirdsilicon nitride layers) and silicon oxide layers SO3-1 to SO3-n(hereinafter, third silicon oxide layers) which are overlapped with thebending area FA. The third silicon nitride layers SN3-1 to SN3-n and thethird silicon oxide layers SO3-1 to SO3-n are stacked alternately.

Substantially, the third silicon nitride layers SN3-1 to SN3-n and thethird silicon oxide layers SO3-1 to SO3-n may have the sameconfiguration (layer structure and/or thickness, etc.) as the firstsilicon nitride layers SN1-1 to SN1-n and the first silicon oxide layersSO1-1 to SO1-n in FIG. 9. Therefore, even if a bending stress greaterthan yield strength is applied to the barrier layer BRL-1 when theflexible display panel DP is bent in the bending area FA, fracture ofthe barrier layer BRL-1 may be prevented.

The barrier layer BRL-1 includes at least one silicon nitride layer SN4(hereinafter, a fourth silicon nitride layer) and at least one siliconoxide layer SO4 (hereinafter, a fourth silicon oxide layer) which areoverlapped with the surrounding area SA. The fourth silicon oxide layerSO4 is overlapped with the fourth silicon nitride layer SN4. In FIG.11A, a barrier layer BRL-1 that includes one fourth silicon oxide layerSO4 and one fourth silicon nitride layer SN4 stacked thereon wasillustrated.

The fourth silicon nitride layer SN4 has a thickness greater than thoseof the third silicon nitride layers SN3-1 to SN3-n, and the fourthsilicon oxide layer SO4 has a thickness greater than those of the thirdsilicon oxide layers SO3-1 to SO3-n. By designing the barrier layerBRL-1 differently depending on the bending area FA and the surroundingarea SA, strength of the flexible display panel DP may be maintained andfracture in the bending area FA may be prevented at the same time.

The barrier layer BRL-1 may be provided by means of chemical vapordeposition, thermal deposition, sputtering, or the like. Using two typesof masks, a silicon nitride layer and a silicon oxide layer may beprovided in each of the surrounding area SA and the bending area FA.

As illustrated in FIG. 11B, a boundary area BA may be defined betweenthe bending area FA and the surrounding area SA. The third siliconnitride layers SN3-1 to SN3-n and the third silicon oxide layers SO3-1to SO3-n are spaced from the fourth silicon oxide layer SO4 and thefourth silicon nitride layer SN4 with the boundary layer BA disposedtherebetween. When viewed from the top, the barrier layer BRL-10 appearsto include a slit defined in the boundary area BA. Although notillustrated in FIG. 11B, a substance which constitutes a layer (forexample, a first insulation layer 12 (refer to FIGS. 7 and 8)) stackedon the barrier layer BRL-10 may be filled into the slit. The silt cutsoff bending stress occurred in the barrier layer BRL-10 along the firstdirection DR1.

FIGS. 12A and 12B are expanded views of a buffer layer according to anembodiment of the inventive concept. Hereinafter, a buffer layer will bedescribed in detail with reference to FIGS. 12A and 12B.

As illustrated in FIG. 12A, a buffer layer BFL-1 according to thisembodiment has different layer structures by area. The buffer layerBFL-1 includes silicon nitride layers SN5-1 to SN5-m (hereinafter, fifthsilicon nitride layers) and silicon oxide layers SO5-1 to SO5-m(hereinafter, fifth silicon oxide layers) which are overlapped with thebending area FA. Substantially, the fifth silicon nitride layers SN5-1to SN5-m and the fifth silicon oxide layers SO5-1 to SO5-m may have thesame configuration (layer structure and/or thickness, etc.) as thesecond silicon nitride layers SN2-1 to SN2-m and the second siliconoxide layers SO2-1 to SO2-m in FIG. 10. Therefore, even though bendingstress greater than yield strength is applied to the buffer layer BFL-1when the flexible display panel DP is bent in the bending area FA,fracture of the buffer layer BFL-1 may be prevented.

The buffer layer BFL-1 includes at least one silicon nitride layer SN6(hereinafter, a sixth silicon nitride layer) and at least one siliconoxide layer SO6 (hereinafter, a sixth silicon oxide layer) which areoverlapped with the surrounding area SA. The sixth silicon nitride layerSN6 has a thickness greater than those of the fifth silicon nitridelayers SN5-1 to SN5-m, and the sixth silicon oxide layer SO6 has athickness greater than those of the fifth silicon oxide layers SO5-1 toSO5-m.

The buffer layer BFL-1 may be provided by means of chemical vapordeposition, thermal deposition, sputtering, or the like. Using two typesof masks, a silicon nitride layer and a silicon oxide layer may bestacked in the surrounding area SA and the bending area FA withdifferent structures.

As illustrated in FIG. 12B, a boundary area BA may be defined betweenthe bending area FA and the surrounding area SA. The fifth siliconnitride layers SN5-1 to SN5-m and the fifth silicon oxide layers SO5-1to SO5-m are spaced from the sixth silicon oxide layer SO6 and the sixthsilicon nitride layer SN6 with the boundary layer BA disposedtherebetween. When viewed from the top, the buffer layer BFL-10 appearsto include a slit defined in the boundary area BA. Although notillustrated in FIG. 12B, a substance which constitutes a layer (forexample, a first insulation layer 12 (refer to FIGS. 7 and 8)) stackedon the buffer layer BFL-10 may be filled into the slit.

FIG. 13 is an expanded view of a barrier layer according to anembodiment of the inventive concept. Hereinafter, a barrier layer willbe described in detail with reference to FIG. 13.

A barrier layer BRL-2 according to this embodiment includes at least onehardness strengthening layer SL. The hardness strengthening layer SLincludes at least any one of graphene, graphene oxide, or carbonnanotube. The hardness strengthening layer SL compensate for reducedhardness of a barrier layer having a multi-layer structure as comparedwith a single layer structure. The hardness strengthening layer SLprevents defects (generally called stamp defects) caused by a largeforce applied to a local area.

FIG. 13 exemplarily illustrates the barrier layer BRL-2, which furtherincludes the hardness strengthening layers SL disposed between siliconnitride layers and silicon oxide layers adjacent to each other, ascompared with a barrier layer BRL in FIG. 9. The number of the hardnessstrengthening layers SL may be changed.

In one embodiment, the hardness strengthening layer SL may be disposedin the bending area FA of the barrier layers BRL-1 and BRL-10 in FIGS.11A and 11B. The hardness strengthening layer SL may compensate forreduced hardness of the bending area FA as compared with the surroundingarea SA.

In one embodiment, the buffer layers BFL, BFL-1, and BFL-10 in FIGS. 10,12A, and 12B may also further include the hardness strengthening layerSL. Particularly, the buffer layers BFL-1 and BFL-10 in FIGS. 12A and12B may further include the hardness strengthening layer SL disposed inthe bending area FA.

Accordingly, the barrier layer protects the pixel from impuritiesintroduced from the outside or come out from a base member. Furthermore,the barrier layer blocks moisture from being introduced into the pixelfrom outsides. The buffer layer enhances properties of the thin filmtransistor as compared with the barrier layer.

The barrier layer and the buffer layer include silicon nitride layersand silicon oxide layers which are disposed alternately. Thereby, thebending stiffness of each of the barrier layer and the buffer layer isreduced.

Since the silicon nitride layers each has a thickness less than or equalto 400 Å, and the silicon oxide layers each has a thickness less than orequal to 650 Å, the silicon nitride layers and the silicon oxide layershave plasticity in a certain range of bending stress (tensile stress orcompressive stress) greater than yield strength. Therefore, fracture ofthe barrier layer and the buffer layer may be prevented even thoughbending stress greater than yield strength is applied thereto.

By designing the layer structures of the barrier layer and the bufferlayer differently depending on the bending area and the surroundingarea, strength of the flexible display panel may be maintained anddefects in the bending area may be prevented at the same time.

Layer structures of the barrier layers BRL, BRL-1, BRL-10, and BRL-2 andthe buffer layers BFL, BFL-1, and BFL-10 may also be applied to thefirst insulation layer 12 (see FIGS. 7 and 8) or the second insulationlayer 14 see FIGS. 7 and 8).

Above, although the invention concept was described with reference toexemplary embodiments thereof, those skilled in the art or those ofordinary skill in the art will understand that the present invention maybe amended or modified without departing from the spirit and scope ofthe invention as defined by accompanying claims.

Therefore, technical scope of the inventive concept should not belimited to detailed descriptions in this specification, but determinedby the claims.

What is claimed is:
 1. A flexible display panel including a bending areaand a peripheral area adjacent to the bending area, the flexible displaypanel comprising: a base member; a barrier layer on the base member; anda pixel on the barrier layer and including a thin film transistor and adisplay element connected to the thin film transistor, wherein thebarrier layer includes at least one first silicon nitride layeroverlapped with the bending area, at least one first silicon oxide layeroverlapped with the bending area, at least one second silicon nitridelayer overlapped with the peripheral area, and at least one secondsilicon oxide layer overlapped with the second silicon nitride layer,and wherein the second silicon nitride layer has a thickness greaterthan the thickness of the first silicon nitride layer, and the secondsilicon oxide layer has a thickness greater than the thickness of thefirst silicon oxide layer.
 2. The flexible display panel of claim 1,wherein the peripheral area and the bending area of the barrier layerhave substantially an equal thickness.
 3. The flexible display panel ofclaim 1, further comprising a buffer layer on the barrier layer andcontacting the thin film transistor.
 4. The flexible display panel ofclaim 3, wherein the buffer layer includes at least one third siliconnitride layer overlapped with the bending area, at least one thirdsilicon oxide layer overlapped with the bending area, at least onefourth silicon nitride layer overlapped with the peripheral area, and atleast one fourth silicon oxide layer overlapped with the fourth siliconnitride layer, and wherein the fourth silicon nitride layer has athickness greater than the thickness of the third silicon nitride layer,and wherein the fourth silicon oxide layer has a thickness greater thanthe thickness of the third silicon oxide layer.
 5. The flexible displaypanel of claim 4, wherein the peripheral area and the bending area ofthe buffer layer have substantially an equal thickness.
 6. The flexibledisplay panel of claim 5, wherein a total thickness of the first siliconnitride layers is less than a total thickness of the first silicon oxidelayers, and wherein a total thickness of the third silicon nitridelayers is greater than a total thickness of the third silicon oxidelayers.
 7. The flexible display panel of claim 3, wherein at least oneof the barrier layer and the buffer layer includes a hardnessstrengthening layer overlapped with the bending area.
 8. The flexibledisplay panel of claim 1, further comprising a boundary area which isdefined between the bending area and the peripheral area, wherein thefirst silicon nitride layers and the first silicon oxide layers arespaced from the second silicon nitride layer and the second siliconoxide layer, respectively, with the boundary area located therebetween.9. The flexible display panel of claim 7, further comprising aninsulation layer disposed on the barrier layer, wherein the boundaryarea comprises the same material as the insulating layer.
 10. Theflexible display panel of claim 7, wherein the flexible display panel isbent around a bending axis extending along a first direction, and theboundary area extends along the first direction.
 11. The flexibledisplay panel of claim 1, wherein the first silicon nitride layer has athickness less than or equal to about 400 Å, and wherein the firstsilicon oxide layer has a thickness less than or equal to about 650 Å.12. A flexible display panel comprising: a base member; a barrier layeron the base member, wherein the barrier layer includes a first hardnessstrengthening layer; and a pixel on the barrier layer and including athin film transistor and a display element connected to the thin filmtransistor, wherein the barrier layer includes at least one firstsilicon nitride layer and at least one first silicon oxide layer, andthe first hardness strengthening layer is located between a firstsilicon nitride layer of the at least one first silicon nitride layerand an adjacent first silicon oxide layer of the at least one firstsilicon oxide layer and comprises a material different from the firstsilicon nitride layer and the adjacent first silicon oxide layer, andwherein the first hardness strengthening layer comprises at least one ofgraphene, graphene oxide, or carbon nanotube.
 13. The flexible displaypanel of claim 12, wherein each of the at least one first siliconnitride layer has an equal thickness, and wherein each of the at leastone first silicon oxide layer has an equal thickness.
 14. The flexibledisplay panel of claim 12, further comprising a buffer layer on thebarrier layer and contacting the thin film transistor, wherein thebuffer layer includes a second hardness strengthening layer.